This car 2005 S40, the fan is not coming on by the temperature sensor until it get to 227 fahrenheit hotness before the ecm turn on the fan, and by then the water will over boil,

i have replace the engine coolant temperature sensor, yet still, the thermostat also have being replace yet still, the fan does not come on at 100 degree but 227 Fahrenheit and this make the car overheat and get the water boiling and getting off from the expansion tank,

one thing that i have seen is that when i unplug the ect sensor the fan come on immediately, and it does not boil as well.

please what might be causing the system not to start at 100 degree but rather goes to 227 Fahrenheit before, which to me is too much and the engine also boil.

Further testing on the sensor, in hot boiling water on stove with DMM shows that

at boiling temperature i get 184 ohms reading on the sensor..

this reading should even trigger the fan on, but it wont do so,

i picked up normal ohms resistor of 150 ohms, when i plug this to the engine sensor harness, the fan comes on, please advice me what might be causing this, at least 184 should still shot out the fan, but it does not but when i put the ohms resistor and start the car, immediately the fan come on

What brand of ECT did you replace and what thermostat?
Not on our S40's but on earlier Volvo's I had similar problems with some aftermarket parts for these... only good quality OEM works... I would look into that- could be your problem. Plug on the ECT connector can also get corroded so check for that and that there is no black/burned connections.